services/keep-web/handler.go

   1 // Copyright (C) The Arvados Authors. All rights reserved.
   2 //
   3 // SPDX-License-Identifier: AGPL-3.0
   4
   5 package main
   6
   7 import (
   8         "encoding/json"
   9         "fmt"
  10         "html"
  11         "html/template"
  12         "io"
  13         "log"
  14         "net/http"
  15         "net/url"
  16         "os"
  17         "sort"
  18         "strconv"
  19         "strings"
  20         "sync"
  21
  22         "git.curoverse.com/arvados.git/sdk/go/arvados"
  23         "git.curoverse.com/arvados.git/sdk/go/arvadosclient"
  24         "git.curoverse.com/arvados.git/sdk/go/auth"
  25         "git.curoverse.com/arvados.git/sdk/go/health"
  26         "git.curoverse.com/arvados.git/sdk/go/httpserver"
  27         "git.curoverse.com/arvados.git/sdk/go/keepclient"
  28         "golang.org/x/net/webdav"
  29 )
  30
  31 type handler struct {
  32         Config        *Config
  33         clientPool    *arvadosclient.ClientPool
  34         setupOnce     sync.Once
  35         healthHandler http.Handler
  36         webdavLS      webdav.LockSystem
  37 }
  38
  39 // parseCollectionIDFromDNSName returns a UUID or PDH if s begins with
  40 // a UUID or URL-encoded PDH; otherwise "".
  41 func parseCollectionIDFromDNSName(s string) string {
  42         // Strip domain.
  43         if i := strings.IndexRune(s, '.'); i >= 0 {
  44                 s = s[:i]
  45         }
  46         // Names like {uuid}--collections.example.com serve the same
  47         // purpose as {uuid}.collections.example.com but can reduce
  48         // cost/effort of using [additional] wildcard certificates.
  49         if i := strings.Index(s, "--"); i >= 0 {
  50                 s = s[:i]
  51         }
  52         if arvadosclient.UUIDMatch(s) {
  53                 return s
  54         }
  55         if pdh := strings.Replace(s, "-", "+", 1); arvadosclient.PDHMatch(pdh) {
  56                 return pdh
  57         }
  58         return ""
  59 }
  60
  61 var urlPDHDecoder = strings.NewReplacer(" ", "+", "-", "+")
  62
  63 // parseCollectionIDFromURL returns a UUID or PDH if s is a UUID or a
  64 // PDH (even if it is a PDH with "+" replaced by " " or "-");
  65 // otherwise "".
  66 func parseCollectionIDFromURL(s string) string {
  67         if arvadosclient.UUIDMatch(s) {
  68                 return s
  69         }
  70         if pdh := urlPDHDecoder.Replace(s); arvadosclient.PDHMatch(pdh) {
  71                 return pdh
  72         }
  73         return ""
  74 }
  75
  76 func (h *handler) setup() {
  77         h.clientPool = arvadosclient.MakeClientPool()
  78
  79         keepclient.RefreshServiceDiscoveryOnSIGHUP()
  80
  81         h.healthHandler = &health.Handler{
  82                 Token:  h.Config.ManagementToken,
  83                 Prefix: "/_health/",
  84         }
  85
  86         // Even though we don't accept LOCK requests, every webdav
  87         // handler must have a non-nil LockSystem.
  88         h.webdavLS = &noLockSystem{}
  89 }
  90
  91 func (h *handler) serveStatus(w http.ResponseWriter, r *http.Request) {
  92         status := struct {
  93                 cacheStats
  94                 Version string
  95         }{
  96                 cacheStats: h.Config.Cache.Stats(),
  97                 Version:    version,
  98         }
  99         json.NewEncoder(w).Encode(status)
 100 }
 101
 102 // updateOnSuccess wraps httpserver.ResponseWriter. If the handler
 103 // sends an HTTP header indicating success, updateOnSuccess first
 104 // calls the provided update func. If the update func fails, a 500
 105 // response is sent, and the status code and body sent by the handler
 106 // are ignored (all response writes return the update error).
 107 type updateOnSuccess struct {
 108         httpserver.ResponseWriter
 109         update     func() error
 110         sentHeader bool
 111         err        error
 112 }
 113
 114 func (uos *updateOnSuccess) Write(p []byte) (int, error) {
 115         if uos.err != nil {
 116                 return 0, uos.err
 117         }
 118         if !uos.sentHeader {
 119                 uos.WriteHeader(http.StatusOK)
 120         }
 121         return uos.ResponseWriter.Write(p)
 122 }
 123
 124 func (uos *updateOnSuccess) WriteHeader(code int) {
 125         if !uos.sentHeader {
 126                 uos.sentHeader = true
 127                 if code >= 200 && code < 400 {
 128                         if uos.err = uos.update(); uos.err != nil {
 129                                 code := http.StatusInternalServerError
 130                                 if err, ok := uos.err.(*arvados.TransactionError); ok {
 131                                         code = err.StatusCode
 132                                 }
 133                                 log.Printf("update() changes response to HTTP %d: %T %q", code, uos.err, uos.err)
 134                                 http.Error(uos.ResponseWriter, uos.err.Error(), code)
 135                                 return
 136                         }
 137                 }
 138         }
 139         uos.ResponseWriter.WriteHeader(code)
 140 }
 141
 142 var (
 143         writeMethod = map[string]bool{
 144                 "COPY":   true,
 145                 "DELETE": true,
 146                 "MKCOL":  true,
 147                 "MOVE":   true,
 148                 "PUT":    true,
 149                 "RMCOL":  true,
 150         }
 151         webdavMethod = map[string]bool{
 152                 "COPY":     true,
 153                 "DELETE":   true,
 154                 "MKCOL":    true,
 155                 "MOVE":     true,
 156                 "OPTIONS":  true,
 157                 "PROPFIND": true,
 158                 "PUT":      true,
 159                 "RMCOL":    true,
 160         }
 161         browserMethod = map[string]bool{
 162                 "GET":  true,
 163                 "HEAD": true,
 164                 "POST": true,
 165         }
 166 )
 167
 168 // ServeHTTP implements http.Handler.
 169 func (h *handler) ServeHTTP(wOrig http.ResponseWriter, r *http.Request) {
 170         h.setupOnce.Do(h.setup)
 171
 172         var statusCode = 0
 173         var statusText string
 174
 175         remoteAddr := r.RemoteAddr
 176         if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
 177                 remoteAddr = xff + "," + remoteAddr
 178         }
 179
 180         w := httpserver.WrapResponseWriter(wOrig)
 181         defer func() {
 182                 if statusCode == 0 {
 183                         statusCode = w.WroteStatus()
 184                 } else if w.WroteStatus() == 0 {
 185                         w.WriteHeader(statusCode)
 186                 } else if w.WroteStatus() != statusCode {
 187                         httpserver.Log(r.RemoteAddr, "WARNING",
 188                                 fmt.Sprintf("Our status changed from %d to %d after we sent headers", w.WroteStatus(), statusCode))
 189                 }
 190                 if statusText == "" {
 191                         statusText = http.StatusText(statusCode)
 192                 }
 193                 httpserver.Log(remoteAddr, statusCode, statusText, w.WroteBodyBytes(), r.Method, r.Host, r.URL.Path, r.URL.RawQuery)
 194         }()
 195
 196         if strings.HasPrefix(r.URL.Path, "/_health/") && r.Method == "GET" {
 197                 h.healthHandler.ServeHTTP(w, r)
 198                 return
 199         }
 200
 201         if method := r.Header.Get("Access-Control-Request-Method"); method != "" && r.Method == "OPTIONS" {
 202                 if !browserMethod[method] && !webdavMethod[method] {
 203                         statusCode = http.StatusMethodNotAllowed
 204                         return
 205                 }
 206                 w.Header().Set("Access-Control-Allow-Headers", "Authorization, Content-Type, Range")
 207                 w.Header().Set("Access-Control-Allow-Methods", "COPY, DELETE, GET, MKCOL, MOVE, OPTIONS, POST, PROPFIND, PUT, RMCOL")
 208                 w.Header().Set("Access-Control-Allow-Origin", "*")
 209                 w.Header().Set("Access-Control-Max-Age", "86400")
 210                 statusCode = http.StatusOK
 211                 return
 212         }
 213
 214         if !browserMethod[r.Method] && !webdavMethod[r.Method] {
 215                 statusCode, statusText = http.StatusMethodNotAllowed, r.Method
 216                 return
 217         }
 218
 219         if r.Header.Get("Origin") != "" {
 220                 // Allow simple cross-origin requests without user
 221                 // credentials ("user credentials" as defined by CORS,
 222                 // i.e., cookies, HTTP authentication, and client-side
 223                 // SSL certificates. See
 224                 // http://www.w3.org/TR/cors/#user-credentials).
 225                 w.Header().Set("Access-Control-Allow-Origin", "*")
 226                 w.Header().Set("Access-Control-Expose-Headers", "Content-Range")
 227         }
 228
 229         arv := h.clientPool.Get()
 230         if arv == nil {
 231                 statusCode, statusText = http.StatusInternalServerError, "Pool failed: "+h.clientPool.Err().Error()
 232                 return
 233         }
 234         defer h.clientPool.Put(arv)
 235
 236         pathParts := strings.Split(r.URL.Path[1:], "/")
 237
 238         var stripParts int
 239         var targetID string
 240         var tokens []string
 241         var reqTokens []string
 242         var pathToken bool
 243         var attachment bool
 244         credentialsOK := h.Config.TrustAllContent
 245
 246         if r.Host != "" && r.Host == h.Config.AttachmentOnlyHost {
 247                 credentialsOK = true
 248                 attachment = true
 249         } else if r.FormValue("disposition") == "attachment" {
 250                 attachment = true
 251         }
 252
 253         if targetID = parseCollectionIDFromDNSName(r.Host); targetID != "" {
 254                 // http://ID.collections.example/PATH...
 255                 credentialsOK = true
 256         } else if r.URL.Path == "/status.json" {
 257                 h.serveStatus(w, r)
 258                 return
 259         } else if len(pathParts) >= 1 && strings.HasPrefix(pathParts[0], "c=") {
 260                 // /c=ID[/PATH...]
 261                 targetID = parseCollectionIDFromURL(pathParts[0][2:])
 262                 stripParts = 1
 263         } else if len(pathParts) >= 2 && pathParts[0] == "collections" {
 264                 if len(pathParts) >= 4 && pathParts[1] == "download" {
 265                         // /collections/download/ID/TOKEN/PATH...
 266                         targetID = parseCollectionIDFromURL(pathParts[2])
 267                         tokens = []string{pathParts[3]}
 268                         stripParts = 4
 269                         pathToken = true
 270                 } else {
 271                         // /collections/ID/PATH...
 272                         targetID = parseCollectionIDFromURL(pathParts[1])
 273                         tokens = h.Config.AnonymousTokens
 274                         stripParts = 2
 275                 }
 276         }
 277
 278         if targetID == "" {
 279                 statusCode = http.StatusNotFound
 280                 return
 281         }
 282
 283         formToken := r.FormValue("api_token")
 284         if formToken != "" && r.Header.Get("Origin") != "" && attachment && r.URL.Query().Get("api_token") == "" {
 285                 // The client provided an explicit token in the POST
 286                 // body. The Origin header indicates this *might* be
 287                 // an AJAX request, in which case redirect-with-cookie
 288                 // won't work: we should just serve the content in the
 289                 // POST response. This is safe because:
 290                 //
 291                 // * We're supplying an attachment, not inline
 292                 //   content, so we don't need to convert the POST to
 293                 //   a GET and avoid the "really resubmit form?"
 294                 //   problem.
 295                 //
 296                 // * The token isn't embedded in the URL, so we don't
 297                 //   need to worry about bookmarks and copy/paste.
 298                 tokens = append(tokens, formToken)
 299         } else if formToken != "" && browserMethod[r.Method] {
 300                 // The client provided an explicit token in the query
 301                 // string, or a form in POST body. We must put the
 302                 // token in an HttpOnly cookie, and redirect to the
 303                 // same URL with the query param redacted and method =
 304                 // GET.
 305                 h.seeOtherWithCookie(w, r, "", credentialsOK)
 306                 return
 307         }
 308
 309         targetPath := pathParts[stripParts:]
 310         if tokens == nil && len(targetPath) > 0 && strings.HasPrefix(targetPath[0], "t=") {
 311                 // http://ID.example/t=TOKEN/PATH...
 312                 // /c=ID/t=TOKEN/PATH...
 313                 //
 314                 // This form must only be used to pass scoped tokens
 315                 // that give permission for a single collection. See
 316                 // FormValue case above.
 317                 tokens = []string{targetPath[0][2:]}
 318                 pathToken = true
 319                 targetPath = targetPath[1:]
 320                 stripParts++
 321         }
 322
 323         if tokens == nil {
 324                 if credentialsOK {
 325                         reqTokens = auth.NewCredentialsFromHTTPRequest(r).Tokens
 326                 }
 327                 tokens = append(reqTokens, h.Config.AnonymousTokens...)
 328         }
 329
 330         if len(targetPath) > 0 && targetPath[0] == "_" {
 331                 // If a collection has a directory called "t=foo" or
 332                 // "_", it can be served at
 333                 // //collections.example/_/t=foo/ or
 334                 // //collections.example/_/_/ respectively:
 335                 // //collections.example/t=foo/ won't work because
 336                 // t=foo will be interpreted as a token "foo".
 337                 targetPath = targetPath[1:]
 338                 stripParts++
 339         }
 340
 341         forceReload := false
 342         if cc := r.Header.Get("Cache-Control"); strings.Contains(cc, "no-cache") || strings.Contains(cc, "must-revalidate") {
 343                 forceReload = true
 344         }
 345
 346         var collection *arvados.Collection
 347         tokenResult := make(map[string]int)
 348         for _, arv.ApiToken = range tokens {
 349                 var err error
 350                 collection, err = h.Config.Cache.Get(arv, targetID, forceReload)
 351                 if err == nil {
 352                         // Success
 353                         break
 354                 }
 355                 if srvErr, ok := err.(arvadosclient.APIServerError); ok {
 356                         switch srvErr.HttpStatusCode {
 357                         case 404, 401:
 358                                 // Token broken or insufficient to
 359                                 // retrieve collection
 360                                 tokenResult[arv.ApiToken] = srvErr.HttpStatusCode
 361                                 continue
 362                         }
 363                 }
 364                 // Something more serious is wrong
 365                 statusCode, statusText = http.StatusInternalServerError, err.Error()
 366                 return
 367         }
 368         if collection == nil {
 369                 if pathToken || !credentialsOK {
 370                         // Either the URL is a "secret sharing link"
 371                         // that didn't work out (and asking the client
 372                         // for additional credentials would just be
 373                         // confusing), or we don't even accept
 374                         // credentials at this path.
 375                         statusCode = http.StatusNotFound
 376                         return
 377                 }
 378                 for _, t := range reqTokens {
 379                         if tokenResult[t] == 404 {
 380                                 // The client provided valid token(s), but the
 381                                 // collection was not found.
 382                                 statusCode = http.StatusNotFound
 383                                 return
 384                         }
 385                 }
 386                 // The client's token was invalid (e.g., expired), or
 387                 // the client didn't even provide one.  Propagate the
 388                 // 401 to encourage the client to use a [different]
 389                 // token.
 390                 //
 391                 // TODO(TC): This response would be confusing to
 392                 // someone trying (anonymously) to download public
 393                 // data that has been deleted.  Allow a referrer to
 394                 // provide this context somehow?
 395                 w.Header().Add("WWW-Authenticate", "Basic realm=\"collections\"")
 396                 statusCode = http.StatusUnauthorized
 397                 return
 398         }
 399
 400         kc, err := keepclient.MakeKeepClient(arv)
 401         if err != nil {
 402                 statusCode, statusText = http.StatusInternalServerError, err.Error()
 403                 return
 404         }
 405
 406         var basename string
 407         if len(targetPath) > 0 {
 408                 basename = targetPath[len(targetPath)-1]
 409         }
 410         applyContentDispositionHdr(w, r, basename, attachment)
 411
 412         client := &arvados.Client{
 413                 APIHost:   arv.ApiServer,
 414                 AuthToken: arv.ApiToken,
 415                 Insecure:  arv.ApiInsecure,
 416         }
 417         fs, err := collection.FileSystem(client, kc)
 418         if err != nil {
 419                 statusCode, statusText = http.StatusInternalServerError, err.Error()
 420                 return
 421         }
 422
 423         targetIsPDH := arvadosclient.PDHMatch(targetID)
 424         if targetIsPDH && writeMethod[r.Method] {
 425                 statusCode, statusText = http.StatusMethodNotAllowed, errReadOnly.Error()
 426                 return
 427         }
 428
 429         if webdavMethod[r.Method] {
 430                 if writeMethod[r.Method] {
 431                         // Save the collection only if/when all
 432                         // webdav->filesystem operations succeed --
 433                         // and send a 500 error if the modified
 434                         // collection can't be saved.
 435                         w = &updateOnSuccess{
 436                                 ResponseWriter: w,
 437                                 update: func() error {
 438                                         return h.Config.Cache.Update(client, *collection, fs)
 439                                 }}
 440                 }
 441                 h := webdav.Handler{
 442                         Prefix: "/" + strings.Join(pathParts[:stripParts], "/"),
 443                         FileSystem: &webdavFS{
 444                                 collfs:        fs,
 445                                 writing:       writeMethod[r.Method],
 446                                 alwaysReadEOF: r.Method == "PROPFIND",
 447                         },
 448                         LockSystem: h.webdavLS,
 449                         Logger: func(_ *http.Request, err error) {
 450                                 if err != nil {
 451                                         log.Printf("error from webdav handler: %q", err)
 452                                 }
 453                         },
 454                 }
 455                 h.ServeHTTP(w, r)
 456                 return
 457         }
 458
 459         openPath := "/" + strings.Join(targetPath, "/")
 460         if f, err := fs.Open(openPath); os.IsNotExist(err) {
 461                 // Requested non-existent path
 462                 statusCode = http.StatusNotFound
 463         } else if err != nil {
 464                 // Some other (unexpected) error
 465                 statusCode, statusText = http.StatusInternalServerError, err.Error()
 466         } else if stat, err := f.Stat(); err != nil {
 467                 // Can't get Size/IsDir (shouldn't happen with a collectionFS!)
 468                 statusCode, statusText = http.StatusInternalServerError, err.Error()
 469         } else if stat.IsDir() && !strings.HasSuffix(r.URL.Path, "/") {
 470                 // If client requests ".../dirname", redirect to
 471                 // ".../dirname/". This way, relative links in the
 472                 // listing for "dirname" can always be "fnm", never
 473                 // "dirname/fnm".
 474                 h.seeOtherWithCookie(w, r, r.URL.Path+"/", credentialsOK)
 475         } else if stat.IsDir() {
 476                 h.serveDirectory(w, r, collection.Name, fs, openPath, stripParts)
 477         } else {
 478                 http.ServeContent(w, r, basename, stat.ModTime(), f)
 479                 if r.Header.Get("Range") == "" && int64(w.WroteBodyBytes()) != stat.Size() {
 480                         // If we wrote fewer bytes than expected, it's
 481                         // too late to change the real response code
 482                         // or send an error message to the client, but
 483                         // at least we can try to put some useful
 484                         // debugging info in the logs.
 485                         n, err := f.Read(make([]byte, 1024))
 486                         statusCode, statusText = http.StatusInternalServerError, fmt.Sprintf("f.Size()==%d but only wrote %d bytes; read(1024) returns %d, %s", stat.Size(), w.WroteBodyBytes(), n, err)
 487
 488                 }
 489         }
 490 }
 491
 492 var dirListingTemplate = `<!DOCTYPE HTML>
 493 <HTML><HEAD>
 494   <META name="robots" content="NOINDEX">
 495   <TITLE>{{ .Collection.Name }}</TITLE>
 496   <STYLE type="text/css">
 497     body {
 498       margin: 1.5em;
 499     }
 500     pre {
 501       background-color: #D9EDF7;
 502       border-radius: .25em;
 503       padding: .75em;
 504       overflow: auto;
 505     }
 506     .footer p {
 507       font-size: 82%;
 508     }
 509     ul {
 510       padding: 0;
 511     }
 512     ul li {
 513       font-family: monospace;
 514       list-style: none;
 515     }
 516   </STYLE>
 517 </HEAD>
 518 <BODY>
 519 <H1>{{ .CollectionName }}</H1>
 520
 521 <P>This collection of data files is being shared with you through
 522 Arvados.  You can download individual files listed below.  To download
 523 the entire collection with wget, try:</P>
 524
 525 <PRE>$ wget --mirror --no-parent --no-host --cut-dirs={{ .StripParts }} https://{{ .Request.Host }}{{ .Request.URL }}</PRE>
 526
 527 <H2>File Listing</H2>
 528
 529 {{if .Files}}
 530 <UL>
 531 {{range .Files}}  <LI>{{.Size | printf "%15d  " | nbsp}}<A href="{{.Name}}">{{.Name}}</A></LI>{{end}}
 532 </UL>
 533 {{else}}
 534 <P>(No files; this collection is empty.)</P>
 535 {{end}}
 536
 537 <HR noshade>
 538 <DIV class="footer">
 539   <P>
 540     About Arvados:
 541     Arvados is a free and open source software bioinformatics platform.
 542     To learn more, visit arvados.org.
 543     Arvados is not responsible for the files listed on this page.
 544   </P>
 545 </DIV>
 546
 547 </BODY>
 548 `
 549
 550 type fileListEnt struct {
 551         Name string
 552         Size int64
 553 }
 554
 555 func (h *handler) serveDirectory(w http.ResponseWriter, r *http.Request, collectionName string, fs http.FileSystem, base string, stripParts int) {
 556         var files []fileListEnt
 557         var walk func(string) error
 558         if !strings.HasSuffix(base, "/") {
 559                 base = base + "/"
 560         }
 561         walk = func(path string) error {
 562                 dirname := base + path
 563                 if dirname != "/" {
 564                         dirname = strings.TrimSuffix(dirname, "/")
 565                 }
 566                 d, err := fs.Open(dirname)
 567                 if err != nil {
 568                         return err
 569                 }
 570                 ents, err := d.Readdir(-1)
 571                 if err != nil {
 572                         return err
 573                 }
 574                 for _, ent := range ents {
 575                         if ent.IsDir() {
 576                                 err = walk(path + ent.Name() + "/")
 577                                 if err != nil {
 578                                         return err
 579                                 }
 580                         } else {
 581                                 files = append(files, fileListEnt{
 582                                         Name: path + ent.Name(),
 583                                         Size: ent.Size(),
 584                                 })
 585                         }
 586                 }
 587                 return nil
 588         }
 589         if err := walk(""); err != nil {
 590                 http.Error(w, err.Error(), http.StatusInternalServerError)
 591                 return
 592         }
 593
 594         funcs := template.FuncMap{
 595                 "nbsp": func(s string) template.HTML {
 596                         return template.HTML(strings.Replace(s, " ", "&nbsp;", -1))
 597                 },
 598         }
 599         tmpl, err := template.New("dir").Funcs(funcs).Parse(dirListingTemplate)
 600         if err != nil {
 601                 http.Error(w, err.Error(), http.StatusInternalServerError)
 602                 return
 603         }
 604         sort.Slice(files, func(i, j int) bool {
 605                 return files[i].Name < files[j].Name
 606         })
 607         w.WriteHeader(http.StatusOK)
 608         tmpl.Execute(w, map[string]interface{}{
 609                 "CollectionName": collectionName,
 610                 "Files":          files,
 611                 "Request":        r,
 612                 "StripParts":     stripParts,
 613         })
 614 }
 615
 616 func applyContentDispositionHdr(w http.ResponseWriter, r *http.Request, filename string, isAttachment bool) {
 617         disposition := "inline"
 618         if isAttachment {
 619                 disposition = "attachment"
 620         }
 621         if strings.ContainsRune(r.RequestURI, '?') {
 622                 // Help the UA realize that the filename is just
 623                 // "filename.txt", not
 624                 // "filename.txt?disposition=attachment".
 625                 //
 626                 // TODO(TC): Follow advice at RFC 6266 appendix D
 627                 disposition += "; filename=" + strconv.QuoteToASCII(filename)
 628         }
 629         if disposition != "inline" {
 630                 w.Header().Set("Content-Disposition", disposition)
 631         }
 632 }
 633
 634 func (h *handler) seeOtherWithCookie(w http.ResponseWriter, r *http.Request, location string, credentialsOK bool) {
 635         if formToken := r.FormValue("api_token"); formToken != "" {
 636                 if !credentialsOK {
 637                         // It is not safe to copy the provided token
 638                         // into a cookie unless the current vhost
 639                         // (origin) serves only a single collection or
 640                         // we are in TrustAllContent mode.
 641                         w.WriteHeader(http.StatusBadRequest)
 642                         return
 643                 }
 644
 645                 // The HttpOnly flag is necessary to prevent
 646                 // JavaScript code (included in, or loaded by, a page
 647                 // in the collection being served) from employing the
 648                 // user's token beyond reading other files in the same
 649                 // domain, i.e., same collection.
 650                 //
 651                 // The 303 redirect is necessary in the case of a GET
 652                 // request to avoid exposing the token in the Location
 653                 // bar, and in the case of a POST request to avoid
 654                 // raising warnings when the user refreshes the
 655                 // resulting page.
 656                 http.SetCookie(w, &http.Cookie{
 657                         Name:     "arvados_api_token",
 658                         Value:    auth.EncodeTokenCookie([]byte(formToken)),
 659                         Path:     "/",
 660                         HttpOnly: true,
 661                 })
 662         }
 663
 664         // Propagate query parameters (except api_token) from
 665         // the original request.
 666         redirQuery := r.URL.Query()
 667         redirQuery.Del("api_token")
 668
 669         u := r.URL
 670         if location != "" {
 671                 newu, err := u.Parse(location)
 672                 if err != nil {
 673                         w.WriteHeader(http.StatusInternalServerError)
 674                         return
 675                 }
 676                 u = newu
 677         }
 678         redir := (&url.URL{
 679                 Host:     r.Host,
 680                 Path:     u.Path,
 681                 RawQuery: redirQuery.Encode(),
 682         }).String()
 683
 684         w.Header().Add("Location", redir)
 685         w.WriteHeader(http.StatusSeeOther)
 686         io.WriteString(w, `<A href="`)
 687         io.WriteString(w, html.EscapeString(redir))
 688         io.WriteString(w, `">Continue</A>`)
 689 }